The valley-like channels on Mars are a complete enigma. They resemble pits caused by melting glaciers in Antarctica, but the elevated positions of many of the features are not where we would expect to find flowing water any time soon.

So how did these Martian pits form? Sublimation of carbon dioxide ice has been put forward as an alternative hypothesis, but a new study by a group of scientists in the US suggests that liquid water could actually do the job under the right conditions. What's more, on geological timescales, it could have happened recently, perhaps only 630,000 years ago.

The key is the planet's axis tilt. According to the new temperature and circulation simulation, when this tilt reaches 35 degrees, the density of the atmosphere will cause the surface to briefly rise above freezing. This would be enough to melt some of the snow and ice currently on Mars.
"We know from our research and other people's research that early in the history of Mars there was water flowing across the surface in valley networks and lakes," says planetary scientist Jim Head of Brown University.
"But about 3 billion years ago, all of that liquid water disappeared and Mars became what we call a hyper-arid or polar desert."

Calculations by the research team shed more light on how these troughs started, how much erosion they cause and how far they can extend. The team was able to fit its model to data from the Terra Sirenum region of Mars, matching it to periods when the troughs are thought to have expanded rapidly in the region.
A dual scenario of trough formation, in which channels created by melting ice are then further eroded by the evaporation of CO2 frost. These regions most likely still have reserves of ice trapped beneath the surface and have had much more in the past.
Flowing water erosion fits the characteristics of the Martian landscape better than CO2-related erosion, which has no equivalent that we can study on Earth and does not tend to cause the same effects on the rock it comes into contact with. This type of activity has been observed on present-day Mars through high-resolution satellite imagery.

"Our study shows that the global distribution of troughs is better explained by liquid water over the last million years," says planetary scientist Jay Dickson of the California Institute of Technology.
"Water explains the height distribution of the pits in a way that CO2 cannot. This means that Mars was able to produce enough volume of liquid water to erode the trenches over the last million years, which is very new on the scale of Martian geological history."

The axis tilt of Mars is known to change over time, albeit over hundreds of thousands of years. This movement has previously been associated with ice ages on the red planet.
Melting water on Mars in the relatively recent past could have facilitated the development of organisms, so the research also offers an interesting new perspective on the potential for life on Mars.
Eventually, the planet will return to a 35-degree angle, allowing local patches of liquid water to flow once again.
Going all the way back to the Dry Valleys in Antarctica, life remains in a kind of stasis in the absence of liquid water. It is not unlikely that something similar is happening on Mars.

"Could there be a bridge in terms of liquid water between the early hot and wet periods of Mars and the Mars we see today?" says Head. "Everyone is always looking for environments that might be favourable not only for life to form, but to be preserved and sustained."
"Any microorganisms that might have evolved on early Mars would be in places where they would have been comfortable in ice, and then later in liquid water, where they would also have been comfortable or prosperous."

 

Source: https://www.sciencealert.com/